Quantum Entanglement is Quantum: ZZ Production at the LHC

TL;DR

This paper investigates quantum entanglement in diboson systems at the LHC, analyzing how higher-order corrections affect the quantum properties and the interpretation of these processes as two-qutrit systems.

Contribution

It provides a detailed analysis of quantum entanglement in diboson processes, incorporating higher-order QCD and electroweak corrections and assessing their impact on quantum interpretations.

Findings

NLO QCD corrections preserve the two-qutrit structure but weaken entanglement signals.

Electroweak corrections introduce non-factorizable effects that alter quantum properties.

Event selection strategies can mitigate some correction effects, but challenges remain for Higgs decay channels.

Abstract

Polarization and spin correlations in diboson systems serve as powerful tools for precision tests and searches for new physics. Recently, interpreting these observables through the lens of quantum information, for instance by examining whether the diboson systems exhibit entanglement, has introduced a compelling new dimension to these studies. We analyze the angular coefficients in the processes $pp\to e^+e^-\mu^+\mu^-$ and $h\to e^+e^-\mu^+\mu^-$, incorporating higher-order QCD and electroweak corrections. Guided by the fundamental properties of the spin density matrix, we assess the stability of the two-qutrit interpretation under radiative effects. For the $pp \to e^+e^-\mu^+\mu^-$ process, NLO QCD corrections preserve the two-qutrit structure but weaken entanglement indicators, an effect that can be partially mitigated by jet binning. In contrast, electroweak corrections introduce non-factorizable contributions that modify the quantum properties of the system. While these effects can be largely depleted by selecting events with a double-resonant $ZZ$ structure, such a kinematic handle is not available for Higgs decays. In the $h \to e^+e^-\mu^+\mu^-$ channel, singly-resonant NLO electroweak corrections substantially distort the angular coefficients, challenging the description of these events as a two-qutrit system.